Gas ovens typically control temperature in the cooking chamber of the oven by using a valve to control the rate of gas flow to a gas burner that provides heat energy into the cooking chamber through combustion of the gaseous fuel. Upon starting a gas oven, the cooking chamber is preheated based on the desired set point temperature and, once obtained, the valve is manipulated in an effort to regulate the temperature around the desired set point. More specifically, typically the valve is cycled between completely on and completely off states in an effort to maintain an average temperature at or around the desired set point temperature.
Gas oven appliances used for baking can suffer disadvantages in heat control and distribution compared with oven appliances that use electric heating elements (e.g., resistance based heating elements). One important shortcoming of certain gas ovens can be the very high rate at which heating occurs. While a high heating rate is advantageous in terms of reducing the time for preheating the cooking chamber to the desired temperature, during cooking operations the high heat rate used to maintain the set-point temperature is too fast for certain food loads that cook better at lower heat rates (such as e.g., sugar cookies, cakes, pastries, dough).
Additionally, because of the large flue needed to enable good combustion of the gaseous fuel, a gas oven cools down rapidly when the gas burner is in the off state. This characteristic increases the amount of time during cooking operations such as baking that the burner must be fired (a short cycling period), which also increases the amount of time the food is exposed to a heating rate that is excessive.
FIG. 1 illustrates a plot of the temperature (measured at the oven center—i.e. the center oven temperature or “COT”) versus time for a typical electric oven placed at a set point temperature of 350° F. FIG. 2 illustrates a plot of COT versus time for a typical gas oven placed at a set point temperature of 350° F. As stated, the gas oven operates with higher heating and cooling rates and must also cycle on and off more frequently as compared to the electric oven to maintain similar amplitudes. More specifically, in FIG. 1, the period of the typical electric oven temperature plot is about 6 to 8 minutes, the heating rate is about 8° F. per minute, and the cooling rate is about 4° F. per minute. For FIG. 2, the period of the gas oven temperature plot is about 1 to 2 minutes, the heating rate is about 29° F. per minute, and the cooling rate is about 15° F. per minute.
FIG. 3 sets forth an additional problem that occurs in conventional gas oven operation. Temperature measurements of the oven chamber (COT) are shown over time with a door opening event (DO) shown at approximately 27 minutes. After preheating and then entering a cycling state around the temperature set point, a transient response occurs when the oven door is opened and food is introduced into the cooking chamber. The gas oven drops in temperature as heat escapes due to opening of the door and the addition of a relatively cold food load. As such, the gas oven effectively reverts back to a preheat mode where the gas burner runs on high and then reinitiates cycling around the desired temperature set point temperature. Again, this relatively high rate of heating exceeds the rate that results in optimum baking performance of certain foods. The problem is particularly exacerbated for short cooking cycle foods that bake in only about e.g., 10 minutes. The rapid reheat phase can affect as much as 50% of the baking period. Efforts to offset these responses by adjusting the calibration point of the ovens does not effectively correct the outcome and negatively impacts the cooking times of long cycle foods such as casseroles, meats, etc.
A final issue with certain conventional gas ovens is the tendency for the heat entering the oven to do so in a single flow pattern (a developed flow field). This means the heat circulates through the oven in a similar flow pattern for the bulk of the heating time because the heat source is constant. As a result, heating within the oven and heating of the food loads in particular is not performed uniformly. It is inherent that some portions of the foods will be heated more or less than others with the constant supply of convective heat.
Accordingly, an improved system for gas oven control would be useful. Such an improved system that can also provide more uniform heating of the cooking chamber and foods placed therein would also be useful.